root/trunk/library/numberlist.lgt

:- object(numberlist,
    implements(numberlistp),
    extends(list)).

    :- info([
        version is 1.3,
        author is 'Paulo Moura',
        date is 2008/9/15,
        comment is 'List of numbers predicates.']).

    average([], 0.0).
    average([N| Ns], Average) :-
        average(Ns, 1, N, Average).

    average([], Length, Sum, Average) :-
        Average is Sum / Length.
    average([N| Ns], Lacc, Sacc, Average) :-
        Lacc2 is Lacc + 1,
        Sacc2 is Sacc + N,
        average(Ns, Lacc2, Sacc2, Average).

    min([X| Xs], Min) :-
        min(Xs, X, Min).

    min([], Min, Min).
    min([X| Xs], Aux, Min) :-
        (   X < Aux ->
            min(Xs, X, Min)
        ;   min(Xs, Aux, Min)
        ).

    max([X| Xs], Max) :-
        max(Xs, X, Max).

    max([], Max, Max).
    max([X| Xs], Aux, Max) :-
        (   X > Aux ->
            max(Xs, X, Max)
        ;   max(Xs, Aux, Max)
        ).

    product([X| Xs], Product) :-
        product(Xs, X, Product).

    product([], Product, Product).
    product([X| Xs], Acc, Product) :-
        Acc2 is Acc * X,
        product(Xs, Acc2, Product).

    sum(List, Sum) :-
        sum(List, 0, Sum).

    sum([], Sum, Sum).
    sum([X| Xs], Acc, Sum) :-
        Acc2 is Acc + X,
        sum(Xs, Acc2, Sum).

    valid(-) :-     % catch variables and lists with unbound tails
        !,
        fail.
    valid([]).
    valid([Element| List]) :-
        number(Element),
        valid(List).

:- end_object.